CA1077725A - Process for obtaining metal values by leaching raw sea nodules - Google Patents

Abstract

Abstract of the Disclosure Metal values are extracted from a manganiferous oxide ore, particularly sea nodules, containing non-ferrous metal values selected from the group consisting of nickel, cobalt and copper, by leaching the raw ore in an acidic medium under atmospheric pressure and in the presence of a sulfide to reduce the tetravalent manganese to the soluble divalent state, thereby oxidizing the sulfide to elemental sulfur, and simultaneously to solubilize metal values in the leach solution.

Description

777~S

~ACKGROUND OF TH~ INVENTION
This invention relates to a hydrometallurgical process for extracting metal values from manganiferous oxide ores, and particularly to the extraction of nickel, cobalt, copper, molybdenum, zinc and manganese values fro~ deep sea nodules.
Nodular mineral deposits found in large quanti-ties on the ocean floor are a potential source of metals. The physical and chemical nature of these deposits vary depending on their location. In general, they contain major amounts of manganese and iron and minor amounts of nonferrous metals such as nickel, cobalt and copper. For example, typical deposits can contain up to about 2% nickel, up to about 2~
copper, up to about 1% cobalt, up to about 25~ iron, and up to about 40~ manganese. Since the components of the nodu]es are tied in intimate and complex association they are not amenable to separation by conventional beneficiatlon procedures. For the same reasons, extraction of the valuable metals is difficult.
Various methods have been suggested for extracting metal values from sea nodules. ~mong the proposed processes are those which require a high temperature treatment prior to leaching, e.g. for selective reduction of the nonferrous metals in the ore. U.S. Patent No. 3,471,2~5, for example, involves subjecting the nodules to a H2-CO gas at about 400C
to 1000C prior to the leaching step. Such processes, which have high energy requirements, are becoming increasingly un-attractive.
Other proposed processes such as U.S. Patents No.
3,752,745 and No. 3,773,635 involve chloridizing the metal values be-fore leaching. U.S. Patent No. 3,752,745, for ~777~5 example, uses hydrogen chloride gas at temperatures between 110C. and 600C. before leaching. In addi-tion to the substantial fuel consumption to dry the nodules, forma-tion of metal chloride vapors and particularly wet chlorine gas present a problem. Wet chlorine is a highly corrosive gas which must be reduced to regenerate ~ICl, or purified for marketing. ~lthough directly leaching the nodules wi-th hydrochloric acid in aqueous rnedia would avoid consumption of fuel for drying, formation of chlorine will occur. In general, the chlorination processes which involve drying the nodules and/or the release of chlorine gas are un-desirable.
In accordance with one aspect of this invention, a method has been found which has relatively low energy requirements and which even with chloride leaching, avoids the problems of contending with the disposal of chlorine gas.
In accordance with another aspect of the present invention a process is provided for simultaneously extracting metal values from sea nodules and from mineral sulfides.
By mineral sulfide is meant a naturally occurring sulfidic material found in ore or ore concentrates.
Examples are pyrrhotite, pentlandite, millerite, chalco-pyrite, chalcocite, and the like, or any combination of them.
This aspect of the invention is discussed herein mainly with reference to pyrrhotite as the mineral sulfide.
Pyrrhotite is an iron sulfide mineral having the formula Fen_lSn. The value of "n" varies for different localities. It is often associated with ores of copper, nickel and precious metals, and is mined in large quantities to recover the associated valuable minerals. When pyrrllotite ~7~

is concentrated and separated from these minerals, it i5 impossible to obtain perfect separation. Thus typical pyrrhotite concentrates may contain up to about l.S~ nickel, up to about 0.8~ copper, and up to about 0.1% cobalt.
It is known, as shown in U.S. Patent No. 1,990,229, to utili~e low grade ores such as pyrites as a source of sulfur in sulfur roasting oxidic ores. U.S. Patent No.
3,809,624 purports to use pyrites and pyrrhotite in an oxidative roast step to convert nonferrous values in deep sea nodules to sulfates and iron to Fe2O3. In the latter patent the objective is to convert the sulfide to sulfate and after cooling to leach the sulfate with water. The roasting step is carried out at a temperature of at least 350C, preferably 4~0 to 600C for a period of about 15 hours. Thus the method involves high temperature treatment ~
which the present process seeks to avoid.
According to the embodiment of the present invention in which metal values are simultaneously extracted from sea nodules and from low grade mineral sulfides, a process is provided which has relatively low energy requirements and does not have the problems of chlorine gas evolution associated with chloride leaching of sea nodules. Moreover, by utilizing the low grade sulfide mineral as a reagent to assist in the reductive leach oE the manganiferous oxide ore, metal values can be released from both the oxide and sulfide materials.
Thus, as applied to the treatment of sea nodules and pyrrhotite, the present process offers a route for recovering metal values from both deep sea nodules and pyrrhotite, both of which represent substantial future sources of metals.

SUMMARY OF T~E INVENTION
~ . ~
Generally, the present invention contemplates a process for extracting metal values from raw sea nodules, said sea nodules containing a major amount of manganese and iron, manganese being present in tetravalent fQrm~ and containing a minor amount of nonferrous metals including at least one of the metals nickel, cobalt and copper, comprising subjecting a slurry of raw sea nodules in an aqueous acidic slurry to a reductive leach in the p~esence of a sulfide at reaction temperature to reduce tetravalent manganese to divalent manganese and simultaneously to solubilize metal ~alues in the leaching medium, said sulfide forming elemental sulfur and separating the medium containing dissolved metal values from the residue of the leached sea nodules~ Advantageously, the sulfur is provided in a concentration su~ficient to reduce substantially all the tetravalent manganese to the divalent state, while maximizing the solubilization of the nickel, copper ~nd cobalt. Alternatively, copper may be simultaneously precipitated as sulfide, thus effecting an in-situ separation of copper from nickel, cobalt and manganese~
In particular, the present invention provides a hydrometallurgical p~ocess or extracting nonferrous metal values simultaneously from ; 2a manganiferous sea nodules and a mineral sulfide, said sea nodules containing a major amount of manganese and iron, manganese being present predominantly in the tetravalent state, and a minor amount of nonferrous metals including at least one of the metals nickel, cobalt, and copper, and said mineral ~ulfide containing a minor amount of nonerrous metals comprising:
a) forming a slurry containing a mixture of raw sea nodules and a mineTal sulide in an aqueous acidic medium, said acid : being hydrochloric acid, said mineral sulfide being present in an amount sufficient to reduce su~stantially all the tetravalent manganese to the divalent state while maximizing 3a the solubilization of nickel and cobalt;

. ,, ~4_ 7~7~5 h~ leaching said sea nodules and mineral sulfide at a tel~erature of about 80C~ to about 100C , while maintaining the hydro-chloric acid level at a value to give a predetermined redox potential which will pe~mit a rapid ~ate of reaction with substantially no evolution of C12 or ~2S, to for~t a leach solution containing non ferrous metals extracted from said sea nodules and said mineral sulfide, and elemental sulfur;
and c~ separating said leach solution containing the non-ferrous metal values from the insoluble residue.
The present invention also provides a hydrometallurgical process Por extracting metal values from sea nodules containing tetravalent manganese, and at least one of the metals nickel and cobalt, comprising:
a~ ~orming a slurry of raw sea nodules in an aqueous acidic medium;
supplying hydrogen sulfide to said slurry in an amount suficient to reduce substantially all the tetTavalent manganese to the divalent state while maximizing the solubilization of the nickel and cobalt;

2~ c~ maintaining said slurry at atmospheric pressure, at a t~mperature of about 50C~ to about 80C~, and at a pH of about 1,5 ~o about 3, to extract metal values from said sea nodules into said aqueous acidic medium, thereby formiDg a pregnant leach solution, an insoluble residue and elemental sul~ur; and d~ sepa~ating said pregnant leach solution from the insoluble residue, It is believed, that, in the sea nodules~ which is a complex ore, manganese is present mainly as MnO2 and it is necessary to reduce the Mn 4 to hht to release the manganese and the other nonferrous metals. The sulfide serves as a reduoing agent and preferably substantially all the sulfide moiety is converted to elemental sulfur.
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The sulficle may be provided directly, e.g as a gaseous, liquid or solid sulfide, or may be derived from a mineral, or combinations thereo~. Examples of sulEides used directly are hydrogen sulfide, ammonium sulfides, or alkali metal or alkaline earth metal sulfides such as Na2s~ NaSH, S, KHS, CaS, or a combination thereof. Of these, hydrogen sulfide is preferred. As noted above, the sulfide may also be provided by a mineral sulfide contained in an ore or ore concentrate, e.g. pyrrhotite, pentlandite, millerite, chalcopyrite, chalcocite, and the like ! or any combination thereof. Although the mineral sulfide may be added as the ore per se, in practice it will be employed in the form of a concentrate containing one or more of the mineral sulfides.
The concentrate will usually be in finely divided form, of the order of minus 200 mesh~
Recovery of metal values from the leach solution can be effected by known techniques.
~t is to be noted that herein all materials are, unless otherwise stated, given on a weight basis, and that ; 20 the redox potentials are values measured directly using a platinum vs. standard calomel electrode, stated as Pt/SCE.

BRIEF DESCRIPTION OF DRAWINGS
The accompanying Figures are schematic flow sheets showing the steps for treating sea nodules according to preferred embodiments of the invention.
Figure 1 is directed to a method in which hydrogen sulfide is used directly as the reducing agent in an aqueous hydrochloric or sulfuric acid medium. Figure 2 illustrates the embodiment in which sea nodules are treated with a pyrrhotite concentrate in an aqueous hydrochloric acid medium.

~77'72~

The preferred embodiments of the present invention are discussed with reference to these figures.

DE~SCRIPTION OF PREFERRED EMBODIMENTS
As illustrated in the accompanying E`igures, raw sea nodules are subjected directly to a reductive acid leach under relatively mild conditions. Prior to the leaching step, it is advantageous to reduce the particle size of the nodules. ~he conditions under which the preferred embodi-ments are carried out and the effect of various factors are given below with reference to the Figures.

Particle Size Reduct on The nodules are crushed, ground or otherwise reduced to a fine particle size, e.g. 95~ ~ 48 mesh (1'SS), and preferably Y5% ~ 100 mesh. Although the nodules are porous and ha~e a relatively large surface area, the great tortuosity of the pores in the nodules hinders diffusion of reactants and products. Therefore, it is advantageous to reduce the size of the nodules, thereby making the nodules receptive to complete and rapid reactions.

A. Referring to FIGURE 1 It will be noted that it is not necessary to dry the nodules before they are subjected to reductive leaching. The wet raw nodules are ground and fed directly to an aqueous medium and reduction of the manganese is achieved in the leaching medium.

Reductive Acidic Leach Briefly, this step comprises leaching sea nodules in a dilute aqueous acid in the presence of a controlled ~77725 low concentration of a sulfide, which in the preferred embodiment of Figure 1 is hydrogen sulfide. The acid ernployed is advantageously a mineral acid, e.g. HCl or ~I2S04 .
In accordance with this invention, the purpose of the acid-leach step is the reduction of manganese from Mn+4 to Mn+2 and solubilization of metal values in the leach solution. Elemental sulfur is formed which can be readily concentrated by known flotation techniques and, if desiredr reused for the generation of H2S.
It will be appreciated that the reactions taking place in the acid leach medium are complex and competing.
In general, the desired reaction for the manganese component is the reduction from a tetravalent to a divalent state.
In a hydrochloric acid medium, for example, the desired reaction with respect to MnO2 is:

MnO2 + H2S + 2HCl -- ~ Mncl2 + 2H2O + S
In sulfuric acid, the desired reaction is:

MnO2 ~ H2S + H2 ~ MnS04 + 2H20 + S
According to one embodiment nickel, cobalt and manganese values are selectively separated from copper and iron values, and are extracted as, e.g.,the chlorides or sulfates, depending on the acid used in the process.
It has been found that the desired solubilization of the metals can be achieved by careful control o~ the pH
and redox potential of the leaching slurry. Preferably, HCl is the acid and the metal values are brought into solution as chlorides. The pH of the acid solution is maintained ~L~7~Z5 ; during the process at a value not exceeding about 5, and preferably between about 1.5 to about 3. Below a pEI of about 1.5 there is a danger of chlorine evolution while at a pH of above about 3, the reaction is too slow. At pEI 5 and above and any redox, the reaction wi]l be very slow - at low redox potentials dissolved metal values will be precipitated as sulfides. Adjustment of the pH
is achieved by adding acid to the slurry.
The hydrogen sulfide is added to the slurry at a substantial]y constant xedox pote~tial. The prevailing redox potential determines the activity of sulfide ion in solution and thus affects the overall rate of reaction. To maintain the desired activity, the hydrogen sul~ide is metered into the slurry at a rate which will maintain the redox potential at a positive value at less than about 600mV (millivolts) Pt/SCE, and preferably, between about plus 200 mV(millivolts) and about plus 500 mV. No additional advantage is gained by operating a redox potential below about plus 200 mV. The effect of high redox is strongly related to the pH. At high pEI, the reaction is very slow.
In a chloride medium at low pH, the probability of chlorine evolution increases with increasing redox potential. As noted, adjustment of the redox potential is achieved by regulating the rate of H2S charged to the slurry. ~t any instant, the concentration of sulfide in the leach slurry is extremely low. However, the accumulated consumption of H2S during the leach will be about 5% to about 15~ by weight of the nodules.
By maintaining the pH of the slurry and the redox potential within the disclosed limits, the desired metal values are extracted in solution as salts of the acids, e.g., as chlorides or sulfates.

:~777~5 Selectivity can be achieved by adjusting the pH
and redox potential within specific ranges. The pH and redox levels for selective extraction will be approximately the same for both HCl and H2SO4. It will be noted that nickel, cobalt and manganese are always extracted. However, the copper and iron extraction can be regulated as follows: at low pH and high redox, copper is quantitatively extracted and iron is partially extracted and present as Fe+3 in solution.
At low pH and low redox, copper is partially precipitated as sulfide and iron is extracted and present as Fe+2 in solution. At high pH and high redox, copper is extracted and iron is not solubilized. At high pH and low redox, copper is precipitated as sulfide and iron is partially extracted and present as Fe in solution. Low pH is about 1.5 or less and high pH is of the order of about 2.5 to 3 or higher.
Low redox potentials are of the order of +200 mV and lower.
Thus, for hydrochloric acid leach, low p~, e.g. about 1.5, and high potentials, e.g. about +400 to +500 mV, are most effective for solubilizing copper as well as nickel, cobalt and manganese values. Higher pH's, about 2.5 to 3, and lower potentials, about +200 to +300 mV, do not favor extraction of copper and iron values. Raising the potential above about +300 mV at the higher pH level, tends to suppress iron solubilization, but increases the extraction of copper values. At a pH of about 2.5 to 3 and a redox potential of about +200 to +300 mV, it is possible to precipitate substantial amounts of copper as copper sulfide, which can be recovered as flotation concentrate. This achieves an in-situ separation of Cu from Ni, Co, and manganese values.

1C3777'~5 The acidic leach is preferably carried out at a temperature in the range of about 50C. to about 80C.
Reaction occurs rapidly, e.g. in about 10 to 60 minutes.
At higher temperatures the reactlon is more rapid. It is an advantage of the present process that leaching can be carried out under atmospheric pressure.
In general, the maximum solids content of the leach-slurry will depend on the particular acid, limited by the solubility of the metal salts. Wi-th EICl the maximum solids content will be in excess of about 50~ solids, but with H2SO4, the maximum will onl~ be about 35% solids. A solids content of about 10%, for example, has been found satisfactory.
However, the preferred pulp density for leaching will he about 30~ solids or more.
It will be appreciated that the composition of the acidic leach slurry is continually changing as the ore reacts both with respect to the oxidation state of the metal values and the concentration of the acid. It is a feature of this invention that the desired results can be achieved by a simple effective means viz. by monitoring the pH and the redox potential of the slurry. An advantage of the process is that the reagents can be added continuously by maintaining pH and redox control to minimize dissolution of certain un-desirable elements.
As indicated above, the sulfide, e.g. H2S, is used as an auxiliary reagent to a solubilizing acid such as HCl or H2SO4, and the desired end product of the sulfide is elemental sulfur. Except for the embodiments having selective precipitation of copper, the metal values form mainly soluble salts. When the sulfide concentration is monitored ~777~5 in this way, many disadvantages of the conventional processes can be overcome. For example, the controlled use of hydrogen sulfide in a chloride medium substantially eliminates the problem of chlorine evolution; thus, preventing the need for contending with the highly corrosive gas and also re-ducing the amount of hydrochloric acid reagent required.
The leach step can be conducted batchwise or as a continuous operation and metering of reagent additions by monitoring ph and redox potential can be arranged accordingly, using known techniques. In accordance with one aspect of this invention, the appropriate H25 level is maintained au~omatieally.
The resultant leach solutlon and residue are sepa-rated, e.g. by filtration. The leach solution is treated for recovery of metal values and the residue may be treated for recovery of elemental sulfur and/or metal values. The elemental sulfur may be recycled to regenerate H2S if desired.

Recovery of Metal Values Metal values, e.g., nickel, copper, cobalt, manganese ean be separated and reeovered from the leach solution by known techniques. For example, copper, nickel and cobalt may be separated from strong manganese solution by solvent extraction, ion exchange, hydrolysis, or sulfide preeipitation. The metals can then be recovered as pure products, e.g., by roasting, electrolysis, etc. The manganese can be reeovered by electrolysis, hydrolysis or crystallizing and pyrolizing a manganese salt.

` ~777ZS

Treatment for Iron In preferred embodiments of the present invention, iron is precipitated in the leach residue as hydrated Eerric oxide. Under certain conditions, e.g. low redox and/or low p~l, the precipitation is not comple-te. To remove dissolved iron, the solution is treated to oxidize any ferrous iron to the ferric state and to precipitate hydrated ferric oxide by neutralization.

Recycle of Reagents In a preferred embodiment of this invention, sulfur formed in the reductive leach step is treated to regenerate hydrogen sulfide, which is in turn utilized in the reductive leach step. E'or example, to regenerate ll2S, the sulfur is heated to 300C. or higher in a hydrogen atmosphere.
s. REFERRING TO FIGURE 2 Reductive Acidic Leach Briefly, this step comprises leaching a mixture of sea nodules, and a mineral sulfide, e.g. a pyrrhotite concentrate, in an aqueous acid medium, in which the reagents are controlled so that neither C12 nor ll2S will evolve.
The acid is preferably hydrochloric or sulfuric acid. If mineral sulfides containing iron are used as the reducing agents in sulfuric acid media, some problems can be encountered with the formation and precipitation of basic ferric sulfate compounds. Therefore, hydrochloric acid is preferred when a mineral sulfide containing iron is employed as the reducing agent.

~7'77;Z 5 In accordance with this invention the acid leach step serves to reduce manganese in the nodules from Mn to Mn 2, to solubilize the non-ferrous metals in the nodules in the leach solution, and simultaneously to oxidize sulfide ~ values in the sulfide mineral to elemental sulfur. Also, ; ferrous values (which may be present) in the sulfide mineral are oxidized, and hydrolyzed as ferric hydroxide.
It will be appreciated that the reactions ta]cing place in the acid leach medium are complex and competing.
It is believed, however, that some hydrogen sulfide is formed in the acidic medium and that the hydrogen sulfide reacts with tetravalent manganese, reducing it to the divalent state.
In general, however, the desired overall reaction with respect to the manganese and iron sulfide in aqueous hydro-chloric acid is:
3MnO2 + 2FeS + 6HCl----~ 3MnC12 + Fe203.nH20 + 2S ~ (3-n)H20 During this reaction Cu, Ni, and Co values contained in both ; the nodules and the pyrrhotite are dissolved.
The hydrochloric acid concentration in the leach solution must be maintained suitably low to avoid the evolution of C12 and/or H2S, yet it must be sufficien-tly high to ensure an adequate rate of reaction~ In accordance with one aspect of this invention, the HCl is maintained at a suitable level by monitoring the redox potential at a value below about 700 mV, preferably between about +400 and about +650 mV. ~s noted, the redox potential values are given with reference to a platinum vs. standard calomel electrode (Pt~CE). Below about -~400 mV the rate of reaction is slow, and above about +650 mV the possibility of chlorine evolution increases rapidly. At about ~400 to +S00 mV the pH tends to seek a level of less than about 3. At higher potentials even lower pH values will be obtained.

~L~77725 The mineral sulfide content of the mixture is regulated to provide sufficient reducing agents, e.g.
sulfide or ferrous iron and sulfide, to suppress the formation of C12. Pyrrhotite, for example, is mixed with sea nodules in an amount of about 25~ to about 35~,by weight of the nodules. Hydrochloric acid is added in amount of about 40% to about 60%, by weight, of nodules.
The acid leach is preferably carried out at a temperature in the range of about 80~C. to about 100C.
~eaction occurs fairly rapidly, e.g. in about 1 to 4 hours.
At higher temperatures the reaction is more rapid. It is an advantage that the present reaction can be carried out under atmospheric pressure~ l~owever, elevated temperatures up to 200C resulting in steam pressures up to 1.~5 MPa (210 psig) may be used.
In general, the total solids content of the leach slurry may vary between about 5~ to about 50% solids by weight. A solids content of about 10~, for example, has been found satisfactory, and a solids content of about 30%
is preferred.

It will be appreciated that the composition of the acidic leach slurry is continuously changing as the ore and the sulfidic mineral react. As noted above, i-t is a feature of this invention that the desired results can be achieved by a simple effective means, viz. by monitoring the redox potential of the slurry. An advantage of the process is that reagents can be added continuously by maintaining redox control.
~ hus, the leach step can be conducted batchwise or as a continuous monitoring operation by metering o-f the 3L~77725 redox potential. It will be noted that commercial instru-ments are available ~or this purpose. In the present tests a potentiostat consisting of a redox electrode and a millivolt controller operates such that when the redox potential of the slurry exceeds the des:ired level, the controller opens a valve permitting reagent to enter the reactor. When the redox potential drops belo~ the desired level, the controller closes the valve. In plant practice, both the controller and electrode will be similar in principle, but simpler and more ruggedly designed than laboratory apparatus. The sensitivity of control will depend on the apparatus, but preferably will not exceed + 20 mV.
The resultant leach solution and residue are separated, e.g. by filtration. The leach solution is thereafter, treated for recovery of metal values, the residue for the recovery of elemental sulfur.
Recovery of Metal Values The metal values, e.g. Ni, Cu, Co, Mn, can be separated and recovered from the leach solution by known techniques as indicated previously. For example, one method of treating the pregnant leach solution is as follows: The copper is extrac-ted from the solution by solvent extraction with, for example, LIX 64N (a commercial product manufactured by General Mills Chemicals, Inc., Minneapolis, Minn.). Copper is then stripped from the solvent with spent electrolyte and recovered by electrolysis.
Nickel, cobalt, and any remaining copper are precipitated from the solution at 90C. with a 0.2 ~Pa (30 psig) ~2S.
Nickel and cobalt can be recovered from this precipitate by several well-known techniques. For example, the pre-~1 - 15 -c, j,~

~1 ~37~7Z~

cipitate can be redissolved and cobalt separated from nickel by solvent extraction with, for example, di-2-ethylhexyl phosphoric acid. Both nickel and cobalt can then be recovered by electrolysis.
The solution can -then be, for example, evaporated and cooled to crystallize manganese salts such as manganous chloride or manganous sulfate. Manganese oxides can be recovered from these manganese salts by roasting, for example, at 600C. to 1000C. The respective acids, hydrochloric acid or sulfuric acid, can be regenerated and recovered from the gaseous products of this decomposition and recycled to the leaching stage.
Recovery of S
Elemental sulfur can be recovered from the leach residue by well-known froth flotation techniques. Eor example, either before or after solid-liquid separation the elemental sulfur can be concentrated and separated by adding a suitable commercial frothing agent (if necessary) and sparging air through the slurry. Elemental sulfur is concentrated in a froth phase above the slurry which can easiLy be separated from the slurry. The elemental sulfur can be further purified, if necessary, by, for example, heating the concentrate until the sulfur is molten, and recovering the sulfur by filtration.
The following illustrative examples are given for the purpose of enabling those skilled in the art to have a better understanding of the invention.

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In the Examples raw deep sea nodules containing 0.97% copper, 1.22~ nickel, 0.20% cobalt, 5.35% iron, and 25% manganese are ground to minus 100 mesh and the comminuted nodules are treated to extract the metal values.

EXAMPLE
Samples of the comminuted nodules were added to water to form a slurry containing about 10~ by weight solids. The slurry of raw nodules was heated to about a selected temperature and the pH and redox potential were adjusted by addition of concentrated HCl and H S. A pH
stat was used to monltor the pH of the slurry and to automatically adjust it to a selected value. The pH of the slurry was adjusted at a value between 1.5 and 3.0 by the addition of concentrated HCl. A potentiostat was used to monitor the Redox Potential of the slurry and to automatically adjust it to a selected value between +200 and ~400 mV (Pt/SCE). Deviations from the chosen potential were automatically corrected by sparging H2S through the slurry. The slurry was maintained at these conditions for a selected time.
The slurry was filtered to separate the pregnant leach solution from the leach residue. The leach solution was analyzed for nickel, cobalt, copper, iron and manganese content. The conditions and results of typical test runs are recorded in TABLE I.
The tests show that extraction of nickel, cobalt, copper, iron and manganese values is very high. Copper extractions were temperature dependent, higher copper extraction occurring at higher temperatures.

Selectivity in the HCl medium is shown in Tests 2 and 7 of TABLE I . Test No. 2 shows that at a pH of 2.5 and a redox potential of +300 mV, only 19~ of the copper and ~37~7~S

28~ of the iron are extracted in the leach solution. The extraction of nickel, cobalt and manganese values is high.
Test No. 7 shows that iron can be selectively separated at a pH of 2.5 if the redox potential is maintained at the higher end of the range. Low pH, :i.e. about 1~5 and higher potentials, i.e. about +400 to +500 mV, are most effective for solubilizing all the metal values. Thus, the potentials can be adjusted to maximize the desired result. For example, at a pH of about 2.5 to 3 and at a redox potential of about +200 to +300 mV, copper and iron solubilization can be suppressed, raising the potential brings about in-creased suppression of iron solubilization, but increases the recovery of copper values. I'he marked effect of pH on iron selectivity can be seen in the comparison of Tests 6 and 7.

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777;25 It was noted that there was some conversion of S to SO4 , ranging from about 11~ to about 33%. Generally, the formation of SO4= can be suppressed by operating at higher temperatures and pH with low redox potentials.

EXAMPL~ 2 Samples of comminuted nodules were fed into an acidic leach solution to which H2S was added, using essentially the same procedure as in EXAMPLE 1, except that the acid used was H2So4. The conditions and results of typical test runs are shown in TABLE II.
The results in TABLE II show that with the pH
level in the range 1.5 to 2.5 and the redox control level in the range -~300 to +500 mV, excellent extraction o~ nickel, cobalt and manganese can be obtained. As in HCl me~ia, at high redox control levels (-~500 mV) copper values may be extracted, or at lower redox control levels (+300 mV) simultaneously precipitated as a sulfide. Sulfuric acid consumption, for complete reaction, was 60% to 70% by weight of nodules. The strong interaction between pH and redox control levels is particularly evident, e.g. at pH 1.5 and redox +300 mV, the reaction is complete in 20 minutes while at pH 3.0 and redox 500 mV, the reaction is only 25~ to 30%
complete in 60 minutes.

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_ _ Samples of the comminuted nodules were mixed with a pyrrhotite concentrate (92~ ' 200 mesh) containing, by weight, 0.68% copper, 1.30% nickel, 0.04% cobalt, 35.4 iron, and 35.3~ sulfur to make up a mixture containing 70:30 parts by weight sea nodules: pyrrhotite.
Samples of the mixture of raw sea nodules and pyrrhotite were added to water in an amount to provide a slurry containing 10~ solids.
The slurry, which was continually being stirred, was leached for 1, 2 or 4 hours at 90C. by addition of hydrochloric acid to maintain a constant redox potential at a value of +550 or +650 mV (Pt/SCE) redox potential.
No C12 or H2S evolution was detected. At the end of the designated leach period, the slurry was cooled and thereafter the leach solution was separated from the residue by filtration.
Typical runs and results are tabulated in the TABLE III.
The data show that a high percentage of the Cu, Ni, Co, and Mn values from both the nodules and the pyrrhotite were extracted in the leach solution, and that the iron remained in the residue, while the sulfide was oxidized mainly to elemental sulfur.

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E~ ~~ ~n m ~77'7Z5 The above described process was disclosed with reference to the recovery of me-tal values from sea nodules which are characterized by a high manganese content as well as their highly complex and fine grained structure.
It is believed that metal values such as the nickel and copper components of the nodules are tied to the manganese in a complex way, which is not fully understood and which makes recovery of metal values particularly difficult and poses different problems than in terrestial non-sulfidic nickel ores. However, the present process can also be used for the extraction of nickel, cobalt and copper from other manganiferous oxide ores that contain iron and nonferrous metal values.
Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

,`

Claims (25)

The embodiments of the invention in which exclusive property or privilege is claimed are defined as follows:

1. A process for extracting metal values from raw sea nodules, said sea nodules containing a major amount of manganese and iron, manganese being present in tetravalent form, and containing a minor amount of nonferrous metals including at least one of the metals nickel, cobalt and copper, comprising subjecting a slurry of raw sea nodules in an aqueous acidic slurry to a reductive leach in the presence of a sulfide at reaction temperature to reduce tetravalent manganese to divalent manganese and simultaneously to solubilize metal values in the leaching medium, said sulfide forming elemental sulfur and separating the medium containing dissolved metal values from the residue of the leached sea nodules.

2. A process as described in claim 1, wherein the sulfide is at least one member of the group consisting of hydrogen sulfide, alkali metal sulfides, alkaline earth metal sulfides, ammonium sulfides.

3. A process as described in claim 2, wherein the acid of the acidic slurry is selected from the group con-sisting of hydrochloric acid and sulfuric acid.

4. A process as described in claim 2, wherein the acidic slurry is maintained at a pH in the range of about 1.5 to about 3.

5. A process as described in claim 2, wherein the sulfide is supplied in an amount sufficient to reduce substantially all the tetravalent manganese to the divalent state while maximizing the solubilization of nickel and cobalt.

6. A process as described in claim 5, wherein the sulfide is supplied at a rate to maintain the redox po-tential of the slurry at a value equivalent to between about plus 200 mV to about plus 500 mV (based on Pt/SCE).

7. A process as described in claim 2, wherein the reductive leach is carried out at a temperature in the range of about 50°C. to about 80°C. and under atmospheric pressure.

8. A process as described in claim 2, wherein the sulfide is hydrogen sulfide, and total consumption of hydrogen sulfide during the leach is about 5% to about 15%, based on the weight of the sea nodules.

9. A process as described in claim 3, wherein the pH of said acidic slurry is maintained at about 2 r 5 to about 3, and wherein the sulfide concentration is controlled to maintain a redox potential equivalent to between about plus 400 mV to about plus 500 mV (based on Pt/SCE), whereby nonferrous metals are selectively solubilized and iron values remain predominantly in the residue.

10. A process as described in claim 3, wherein the pH of said acidic slurry is maintained at about 2.5 to about 3, and wherein the redox potential is maintained equivalent to between about plus 200 mV to about plus 300 mV (based on Pt/SCE), whereby copper is selectively maintained in the residue as a sulfide,

11. A process as described in claim 1, wherein the acid of the acidic slurry is hydrochloric acid.

12. A process as described in claim 1, wherein in the reductive leach step the reacted sulfide is oxidized predominantly to elemental sulfur.

13. A process as described in claim 1, wherein the sulfur formed in the reductive leach step is treated to re-generate hydrogen sulfide, and said hydrogen sulfide re-cycled to the reductive leach step.

14. A method as described in claim 1, wherein the sulfide is a mineral sulfide, and wherein nonferrous metal values are simultaneously extracted from the sea nodules and the mineral sulfide.

15. A process according to claim 14 wherein the mineral sulfide comprises pyrrhotite.

16. A process according to claim 14, wherein the aqueous acidic medium comprises hydrochloric acid.

17. A process according to claim 16, wherein the leaching is carried out while maintaining the acid content of the medium at a level selected to insure an adequate rate of reaction with substantially no evolution of Cl2 or H2S.

18. A process according to claim 16, wherein the total amount of hydrochloric acid in the aqueous acidic medium is about 40% to about 60% by weight of the sea nodules.

19. A process according to claim 16, wherein the hydrochloric acid level in the aqueous acidic medium is monitored by maintaining a predetermined redox potential.

20. A process according to claim 19, wherein the redox potential is maintained at a value equivalent to about plus 400 to about plus 650 mV (based on Pt/SCE).

21. A process according to claim 19, wherein the reaction temperature is about 80°C. to about 100°C.

22. A hydrometallurgical process for extracting nonferrous metal values simultaneously from manganiferous sea nodules and a mineral sulfide, said sea nodules contain-ing a major amount of manganese and iron, manganese being present predominantly in the tetravalent state, and a minor amount of nonferrous metals including at least one of the metals nickel, cobalt, and copper, and said mineral sulfide containing a minor amount of nonferrous metals comprising:
a) forming a slurry containing a mixture of raw sea nodules and a mineral sulfide in an aqueous acidic medium, said acid being hydro-chloric acid, said mineral sulfide being present in an amount sufficient to reduce sub-stantially all the tetravalent manganese to the divalent state while maximizing the solubilization of nickel and cobalt;

b) leaching said sea nodules and mineral sulfide at a temperature of about 80°C. to about 100°C., while maintaining the hydrochloric acid level at a value to give a predetermined redox potential which will permit a rapid rate of reaction with substantially no evolution of Cl2 or H2S, to form a leach solution con-taining non-ferrous metals extracted from said sea nodules and said mineral sulfide, and elemental sulfur; and c) separating said leach solution containing the non-ferrous metal values from the insoluble residue.

23. A process according to claim 22, wherein the redox potential is maintained at a value equivalent to about plus 400 to about plus 650 mV (based on a Pt/SCE).

24. A hydrometallurgical process for extracting metal values from sea nodules containing tetravalent manganese, and at least one of the metals nickel and cobalt, comprising:
a) forming a slurry of raw sea nodules in an aqueous acidic medium;

b) supplying hydrogen sulfide to said slurry in an amount sufficient to reduce substantially all the tetravalent manganese to the divalent state while maximizing the solubilization of the nickel and cobalt;

c) maintaining said slurry at atmospheric pressure, at a temperature of about 50°C. to about 80°C., and at a pH of about 1.5 to about 3, to extract metal values from said sea nodules into said aqueous acidic medium, thereby forming a pregnant leach solution, an insoluble residue and elemental sulfur; and d) separating said pregnant leach solution from the insoluble residue.

25. A process according to claim 24, wherein the redox potential of the slurry is maintained at a value between about plus 200 mV and about plus 500 mV (based on Pt/SCE).